Examples of bilaterans
Contrary to creationists dogma that no new genetic information can arise in a genome without god-magic because of some half-baked notion that the Third Law of Thermodynamics, which applies to energy, somehow applies to genetic information, researchers at the Centre for Genomic Regulation (CRG) in Barcelona, Catalunya, Spain, have shown how errors in replication in DNA some 700 million years ago eventually resulted in a vast supergroup of animals (the bilaterans, i.e. animals with bilateral symmetry) including vertebrates (fish, amphibians, reptiles, birds, and mammals), and invertebrates (insects, arthropods, molluscs, worms, echinoderms and many more).
These errors where whole genomes and genes were duplicated, created the condition where the original genes could continue to function while copies of them were free to mutate and produce new genes with new functions, under the control of natural selection which retains anything which is better than what preceded it and quickly eliminate anything which is worse.
Bilaterians are animals that exhibit bilateral symmetry, meaning they can be divided into two equal halves along a single plane. The vast majority of animals on Earth are bilaterians, including many familiar groups such as:The researchers have published their findings in Nature Ecology & Evolution and have explained it in a news release from the Centre for Genomic Regulation (CRG):These are just a few examples, but bilaterians encompass an incredibly diverse range of animal life on Earth.
- Mammals: Humans, dogs, cats, elephants, and dolphins are all examples of bilaterians within the mammalian group.
- Birds: Birds, like sparrows, eagles, penguins, and ostriches, are also bilaterians.
- Reptiles: Snakes, lizards, turtles, and crocodiles exhibit bilateral symmetry.
- Amphibians: Frogs, toads, salamanders, and newts are examples of bilaterians within the amphibian class.
- Fish: Most fish species, including tuna, salmon, sharks, and goldfish, are bilaterians.
- Insects: Butterflies, ants, bees, beetles, and flies are bilaterians within the vast group of insects.
- Arachnids: Spiders, scorpions, ticks, and mites are bilaterians within the arachnid class.
- Mollusks: Snails, slugs, octopuses, and squids exhibit bilateral symmetry.
- Annelids: Earthworms, leeches, and marine worms are examples of bilaterians within the annelid phylum.
- Echinoderms: While not as obvious due to their radial symmetry as adults, echinoderms like sea stars and sea urchins exhibit bilateral symmetry during their larval stages.
700 million years ago, a remarkable creature emerged for the first time. Though it may not have been much to look at by today’s standards, the animal had a front and a back, a top and a bottom. This was a groundbreaking adaptation at the time, and one which laid down the basic body plan which most complex animals, including humans, would eventually inherit.The researchers' paper in Nature Ecology & Evolution is sadly, behind a paywall, with only the abstract available:
The inconspicuous animal resided in the ancient seas of Earth, likely crawling along the seafloor. This was the last common ancestor of bilaterians, a vast supergroup of animals including vertebrates (fish, amphibians, reptiles, birds, and mammals), and invertebrates (insects, arthropods, molluscs, worms, echinoderms and many more).
To this day, more than 7,000 groups of genes can be traced back to the last common ancestor of bilaterians, according to a study of 20 different bilaterian species including humans, sharks, mayflies, centipedes and octopuses. The findings were made by researchers at the Centre for Genomic Regulation (CRG) in Barcelona and are published today in the journal Nature Ecology and Evolution.
Remarkably, the study found that around half of these ancestral genes have since been repurposed by animals for use in specific parts of the body, particularly in the brain and reproductive tissues. The findings are surprising because ancient, conserved genes usually have fundamental, important jobs that are needed in many parts of the body.
When the researchers took a closer look, they found a series of serendipitous ‘copy paste’ errors during bilaterian evolution were to blame. For example, there was a significant moment early in the history of vertebrates. A bunch of tissue-specific genes first appeared coinciding with two whole genome duplication events. Animals could keep one copy for fundamental functions, while the second copy could be used as raw material for evolutionary innovation. Events like these, at varying degrees of scale, occurred constantly throughout the bilaterian evolutionary tree.
The authors of the study found many examples of new, tissue-specific functions made possible by the specialisation of these ancestral genes. For example, the TESMIN and tomb genes, which originated from the same ancestor, ended up independently playing a specialised role in the testis both in vertebrates and insects. Their importance is highlighted by the fact that problems with these genes can disrupt sperm production, affecting fertility in both mice and fruit flies.Our genes are like a vast library of recipes that can be cooked up differently to create or change tissues and organs. Imagine you end up with two copies of a recipe for paella by accident. You can keep and enjoy the original recipe while evolution tweaks the extra copy so that it makes risotto instead. Now imagine the entire recipe book is copied – twice - and the possibilities it opens for evolution. The legacy of these events, which took place hundreds of millions of years ago, lives on in most complex animals today.
Federica Mantica, first author Centre for Genomic Regulation
Barcelona Institute of Science and Technology, Barcelona, Spain.
The specialisation of ancestral genes also laid some foundations for the development of complex nervous systems. For example, in vertebrates, the researchers found genes critical for the formation of myelin sheaths around nerve cells, which are essential for fast nerve signal transmission. In humans they also identified FGF17, which is thought to play an important role in maintaining cognitive functions into old age.
In insects, specific genes became specialised in muscles and in the epidermis for cuticle formation, contributing to their ability to fly. In the skin of octopuses, other genes became specialised to perceive light stimuli, contributing to their ability to change colour, camouflage and communicate with other octopuses. By studying the evolution of species at the tissue level, the study demonstrates that changes in the way genes are used in different parts of the body have played a big role in creating new and unique features in animals. In other words, when genes start acting in specific tissues, it can lead to the development of new physical traits or abilities, which ultimately contributes to animal evolution.
Our work makes us rethink the roles and functions that genes play. It shows us that genes that are crucial for survival and have been preserved through millions of years can also very easily acquire new functions in evolution. It reflects evolution's balancing act between preserving vital roles and exploring new paths.
Professor Manuel Irimia, corresponding-author
Centre for Genomic Regulation
Barcelona Institute of Science and Technology, Barcelona, Spain.
AbstractCreationists are handicapped by their cult's insistence that they must never know any more than the ignorant Bronze Age pastoralists who invented the tales in Genesis to fill the gaps in their knowledge and understanding. So, they know nothing of genetics or how new genetic information can arise in a genome and must assume, like the Bronze Age story-tellers did, that whatever they don't understand must have been done by magic.
Regulation of gene expression is arguably the main mechanism underlying the phenotypic diversity of tissues within and between species. Here we assembled an extensive transcriptomic dataset covering 8 tissues across 20 bilaterian species and performed analyses using a symmetric phylogeny that allowed the combined and parallel investigation of gene expression evolution between vertebrates and insects. We specifically focused on widely conserved ancestral genes, identifying strong cores of pan-bilaterian tissue-specific genes and even larger groups that diverged to define vertebrate and insect tissues. Systematic inferences of tissue-specificity gains and losses show that nearly half of all ancestral genes have been recruited into tissue-specific transcriptomes. This occurred during both ancient and, especially, recent bilaterian evolution, with several gains being associated with the emergence of unique phenotypes (for example, novel cell types). Such pervasive evolution of tissue specificity was linked to gene duplication coupled with expression specialization of one of the copies, revealing an unappreciated prolonged effect of whole-genome duplications on recent vertebrate evolution.
Mantica, F., Iñiguez, L.P., Marquez, Y. et al.
Evolution of tissue-specific expression of ancestral genes across vertebrates and insects. Nat Ecol Evol (2024). https://doi.org/10.1038/s41559-024-02398-5
© 2024 Springer Nature Ltd.
Reprinted under the terms of s60 of the Copyright, Designs and Patents Act 1988.
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